ci: add Gitea Actions workflow with gofmt and test jobs

Add CI workflow at .gitea/workflows/ci.yml triggered on pull_request
with two jobs: fmt (gofmt check) and test (go test ./...).

Fix gofmt issues (import ordering) in 7 files so CI passes from
the start.

Fixes #7

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/mail/smtp.go

@@ -6,10 +6,10 @@ import (
 	"strings"
 	"time"
 
+	"gorm.io/gorm"
 	"thuanle.me/claw-email-bridge/internal/config"
 	"thuanle.me/claw-email-bridge/internal/database"
 	"thuanle.me/claw-email-bridge/internal/logging"
-	"gorm.io/gorm"
 )
 
 // Retry backoff schedule: 1s, 5s, 15s.